Significant first for NASA with probe collision on space rock. ‘If one hits New York, the city no longer exists’

NASA successfully rammed the unmanned spacecraft Dart into asteroid Dimorphos. A big achievement?

‘It was just a question of whether this would work at all. Just imagine: that probe headed toward its target at ten times the speed of a bullet. He only got a good picture of his target half an hour before impact. Then the speck in the distance split in two: Dimorphos orbits a larger asteroid and the probe had to adjust its course, completely autonomously, to hit the smaller one. That worked.

‘It remains to be seen whether the job has also changed as a result. An orbital change of only 1 percent is expected, which you can only observe with telescopes from Earth after a few days or weeks. The effect of the impact depends, among other things, on the composition: if it is a ball of dust made up of loose grit, then the probe makes a less hard move, or rather a hard pebble?

“Another probe came along, Liciacube, and photographed the impact and the grit plume afterwards. That photo is not yet available. And in a year or two, the Hera mission, a European probe that will capture the impact crater on Dimorphos in more detail, will leave. Information about this is important for calibrating the models. After all, if a space rock is really coming towards Earth, you want to be able to predict exactly what time you should hit it and how hard.

‘Another cool thing to think about is that if we’ve managed to change course, this will literally be the first time humans have managed to change the orbit of another celestial body. That’s a nice first.’

If the orbit has indeed changed, will we never have to fear a meteorite impact again?

‘Unfortunately, that doesn’t work. This mission is designed for asteroids with a diameter between 50 and 200 meters: Dimorphos is about 160 meters long. Any larger than that and the operation of this method becomes questionable.

‘In any case, there is no point in ramming something against objects larger than 500 meters. Fortunately, we think we’ve mapped 98 percent of these large asteroids, none on course to hit Earth. If it does happen, then Dart is of no use to you.’

Are asteroids between 50 and 200 meters a real danger?

‘We only know the job of this group in 40 percent of the cases. So it is possible that among the other 60 percent there is an asteroid that is heading towards Earth. NASA says this category of space rocks have “regional destruction potential.” If one pops on top of New York, the city no longer exists.

‘Of course it is much more likely that it will end up in the ocean, the desert or – and that would of course also be very bad – sparsely populated area. But you don’t want to take the risk. Then you have to see the space rock coming at least a year in advance. You only give a small push, so you have to start the change of course well in advance, otherwise it will not be enough.

‘Larger asteroids, depending on their size, can destroy entire countries, cause devastating tsunamis worldwide or block part of the sunlight for years by the particles they throw into the atmosphere. Asteroids larger than 500 meters on average collide with Earth only once every 10 million years. The asteroid that killed the dinosaurs was estimated to be no less than 10 kilometers across. Such an extreme impact only occurs once every 100 million years on average.’

What do we do when a bigger one rages on the earth unexpectedly?

“Then a nuclear bomb goes up. That is by definition an untested method, because you understand why you can’t just test it. Suppose something goes wrong at launch, then you have a big problem. But when a huge space rock hurtles toward Earth, you’ll want to take that risk.

‘You shouldn’t let that bomb hit the rock, like in the movies. Then maybe it will break into pieces and instead of a rock 5 kilometers two miles two and three kilometers will come down to earth. In the movie Armageddon even an oil driller goes there and drills a hole where they put a nuclear weapon. Pretty stupid idea, then. What they would really do is detonate the bomb next door and hope they can push it that way.”